The invention relates to packaging materials. In a preferred form it relates to the use of thermal dye transfer label for the printing of text, graphics, and images applied to a package.
Pressure sensitive labels applied are applied to packages to build brand awareness, show the contents of the package, convey a quality message regarding the contents of a package, and supply consumer information such as directions on product use, or an ingredient listing of the contents. Printing on the pressure sensitive label is typically applied directly to the package or a printed media, typically printed using gravure printing or flexography is applied to the package. The three types of information applied to a pressure sensitive label are text, graphic, and images. Some packages only require one type of information, while other packages require more than one type of information.
Prior art labels that are applied to packages consist of a face stock material, a pressure sensitive adhesive, and a liner. The label substrate consisting of the face stock, pressure sensitive adhesive, and liner are typically laminated and then printed utilizing a variety of nonphotographic printing methods. After printing, the labels are generally protected by an over laminate material or a protective coating. The completed label consisting of a protection layer, printed information, face stock, pressure sensitive adhesive, and liner material is applied to packages utilizing high speed labeling equipment.
Flexography is an offset letterpress technique where the printing plates are made from rubber or photopolymers. The printing on pressure sensitive label is accomplished by the transfer of ink from the raised surface of the printing plate to the surface of the material being printed. The rotogravure method of printing uses a print cylinder with thousands of tiny cells which are below the surface of the printing cylinder. The ink is transferred from the cells when the print cylinder is brought into contact with the pressure sensitive label at the impression roll. Printing inks for flexography or rotogravure include solvent based inks, water based inks, and radiation cured inks. While rotogravure and flexography printing does provide acceptable image quality, these two printing methods require expensive and time-consuming preparation of print cylinders or printing plates which make printing jobs of less than 100,000 units expensive as the setup cost and the cost of the cylinders or printing plates is typically depreciated over the size of the print job.
Recently, digital printing has become a viable method for the printing of information on packages. The term xe2x80x9cdigital printingxe2x80x9d refers to the electronic digital characters or electronic digital images that can be printed by an electronic output device capable of translating digital information. The two main digital printing technologies are ink jet and electrophotography.
The introduction of piezo impulse drop-on-demand (DOD) and thermal DOD ink jet printers in the early 1980""s provided ink jet printing systems. These early printers were very slow, and the ink jet nozzles often clogged. In the 1990""s Hewlett Packard introduced the first monochrome ink jet printer, and, shortly thereafter the introduction of color, wide format ink jet printers enabled businesses to enter the graphic arts market. Today a number of different ink jet technologies are being used for packaging, desktop, industrial, commercial, photographic, and textile applications.
In piezo technology, a piezo crystal is electrically simulated to create pressure waves, which eject ink from the ink chamber. The ink can be electrically charged and deflected in a potential field, allowing the different characters to be created. More recent developments have introduced DOD multiple jets that utilize conductive piezo ceramic material which, when charged, increases the pressure in the channel and forces a drop of ink from the end of the nozzle. This allows for very small droplets of ink to form and be delivered at high speed at very high resolution, approximately 1,000 dpi printing.
Until recently, the use of color pigments in jet inks was uncommon. However, this is changing rapidly. Submicron pigments were developed in Japan for ink jet applications. Use of pigments allows for more temperature resistant inks required for thermal ink jet printers and laminations. Pigmented water-based jet inks are commercially available, and UV-curable jet inks are in development. Pigmented inks have greater lightfastness and water-resistance.
Digital ink jet printing has the potential to revolutionize the printing industry by making short-run, color print jobs more economical. However, the next commercial stage will require significant improvements in ink jet technology; the major hurdle remaining is to improve print speed. Part of this problem is the limitation of the amount of data the printer can handle rapidly. The more complex the design, the slower the printing process. Right now they are about 10 times slower than comparable digital electrostatic printers.
Electrophotography was invented in the 1930""s by Chester Carlson. By the early 1970""s, the development of an electrophotographic color copier was being investigated by many companies. The technology for producing color copiers was already in place, but the market was not. It would take many more years until customer demand for color copies would create the necessary incentive to develop suitable electrostatic color copiers. By the late 1970""s a few companies were using fax machines that could scan a document, reduce the images to electronic signals, send them out over the telephone wire and, using another fax machine, retrieve the electronic signals and print the original image using heat-sensitive papers to produce a printed copy.
In 1993 Indigo and Xeikon introduced commercial digital printing machines targeted on short-run markets that were dominated by sheet-fed lithographic printers. Elimination of intermediate steps associated with negatives and plates used in offset printing provides faster turnaround and better customer service. These digital presses share some of the characteristics of traditional xerography but use very specialized inks. Unlike inks for conventional photocopiers, these inks are made with very small particle size components in the range of 1 xcexcm. Dry toners used in xerography are typically 8-10 xcexcm in size.
In 1995 Indigo introduced the Ominus press designed for printing flexible packaging products. The Ominus uses a digital offset color process called One Shot Color that has six colors. A key improvement has been the use of a special white Electro ink for transparent substrates. The Ominus web-fed digital printing system allows printing of various substrates using an offset cylinder that transfers the color image to the substrate. In principle, this allows perfect register regardless of the substrate being printed; paper, film, and metal can be printed by this process. This digital printing system is based on an electrophotographic process where the electrostatic image is created on the surface of a photoconductor by first charging the photoconductor by charge corona and exposing the photoconductive surface to a light source in image fashion.
The charged electrostatic latent image is then developed using ink containing an opposite charge to that on the image. This part of the process is similar to that of electrostatic toners associated with photocopying machines. The latent charged electrostatic image formed on the photoconductor surface is developed by means of electrophoretic transfer of the liquid toner. This electrostatic toner image is then transferred to a hot blanket, which coalesces the toner and maintains it in a tacky state until it is transferred to the substrate, which cools the ink and produces a tack-free print.
Electro inks typically comprise mineral oil and volatile organic compounds. They are designed so that the thermoplastic resin will fuse at elevated temperatures. In the actual printing process, the resin coalesces and the inks are transferred to the substrate. There is no need to heat the ink to dry it. The ink is deposited on the substrate essentially dry, although it becomes tack-free as it cools and reaches room temperature.
For several decades a magnetic digital technology called xe2x80x9cmagnetographyxe2x80x9d has been under development. This process involves creating electrical images on a magnetic cylinder and using magnetic toners as inks to create the image. The potential advantage of this technology lies in its high press speed. Tests have shown speeds of 200 meters per minute. Although these magnetic digital printers are limited to black-and-white copy, developments of color magnetic inks would make this high-speed digital technology economically feasible. The key to its growth will be further development of the VHSM (very high speed magnetic) drum and the color magnetic inks.
Within the magnetic digital arena, a hybrid system called magnetolithography has been built and tested on narrow web and short-run applications developed by Nipson Printing Systems in Belfort, France. The technology appears to provide high resolution, and tests have been conducted using a silicon-based, high density, magnetographic head. Much more work is necessary in the ink development to bring this system to a competitive position relative to ink jet or electrophotography. However, the fact that it has high speed printing potential makes it an attractive alternate for packaging applications in which today""s ink jet and electrophotography technologies are lagging.
Photographic materials have been known for use as prints for preserving memories for special events such as birthdays and vacations. They also have been utilized for large display materials utilized in advertising. These materials have been known as high quality products that are costly and somewhat delicate, as they would be easily defaced by abrasion, water, or bending. Photographs are traditionally placed in frames, photo albums, and behind protective materials in view of their fragile and delicate nature, as well as their value. They are considered luxury items for the consumers to preserve a record of important events in their lives. They also have been considered as expensive display materials for advertising. In view of their status as luxury items, they have not been utilized in other areas of commerce. In U.S. Pat. No. 6,436,604 (Bourdelais et al.) a silver halide pressure sensitive label is proposed utilizing silver halide imaging layers applied to the surface of an oriented polyolefin base. While the label described in U.S. Pat. No. 6,436,604 is high in quality and provides high quality replication of flesh tones, the wet chemistry used to develop the images makes a silver halide label impractical for converters and end users that do not have the equipment to handle the wet chemistry required for silver halide image processing.
Further, typical label facestock materials comprise oriented polyolefin or polyester sheets. The typical facestock materials also comprise a cavitated layer to provide thickness and stiffness to the label while saving materials. Prior art polyolefin facestock materials are typically low in cost and lower in strength compared to polyester facestock materials which are higher in cost but higher in strength. There remains a need for a dual polymer facestock that combined the polymer properties of both polyolefin and polyester.
Polyolefin films are very useful as protective packaging because they resist tearing and water penetration. However, a significant drawback to their use is the difficulties encountered in writing, with ink, on the film. Typically, polyolefin films have low surface energies which make them nonreceptive to certain inks, particularly water based inks. The water based inks tend to exhibit bad ink wetting properties, in which they fail to form a complete coating on the film; the ink forms into discrete beads, streaks and splotches on the film. Additionally, water based inks tend to dry slowly, smear easily and rub off once dry. These are serious problems particularly when plastic films are used for shipping articles which are often exposed to moisture and rough handling. To overcome these difficulties written matter is usually applied to a paper label which is then attached to the wrapping but this is inconvenient and presents recycling problems because paper recycling is usually incompatible with plastic recycling.
U.S. Pat. No. 4,984,823 (Ishii et al.) discloses a pressure sensitive label having a sublimation transferred image. While the image does have acceptable image quality, the label base comprises cellulose paper or oriented polymer. Both the paper and polymer label bases suffer from low stiffness for high speed label dispensing and the polymer labels are prone to shrinkage at high temperatures in demanding labeling conditions such as automobile engine labeling, labeling of food items that must endure high pasteurization and labeling of items that are exposed to outdoor conditions.
U.S. Pat. Nos. 5,302,574 (Lawerance et al.) and 5,387,571 (Daly et al.) describe thermal dye receiving layers that can achieve thermal printing dye densities of over 0.5 utilizing a mixtures of polyester polymers. The melt extruded polyester dye receiving layer is preferably applied to a cellulose paper base.
There is a need for pressure sensitive labels for application to packages that are high in quality and, at the same time, economical for short runs. There is a further need for the printing of the labels from digital information files without the need for wet processing chemistry.
It is an object of the invention to provide higher quality images to packaging materials.
It is a further object to provide high quality label images that have bright and sharp images.
It is another object to provide a label facestock that combined the desirable properties of both polyolefin and polyester.
These and other objects of the invention are accomplished by an imaging member comprising in order an imaging layer, an upper oriented polymer sheet, a laminating adhesive layer in contact with said upper polymer sheet and also in contact with a lower oriented polymer sheet, and a positioning adhesive in contact with the lower side of said lower polymer sheet.
The invention provides improved image quality for packaging materials. The invention includes a printing method that can print high quality text, graphic and images from a digital file while providing a facestock that strong and able to be machine applied to packages.